U.S. patent application number 12/595856 was filed with the patent office on 2010-03-25 for lash adjuster.
Invention is credited to Hiroshi Bunko, Eiji Maeno, Katsuhisa Yamaguchi.
Application Number | 20100071648 12/595856 |
Document ID | / |
Family ID | 39875482 |
Filed Date | 2010-03-25 |
United States Patent
Application |
20100071648 |
Kind Code |
A1 |
Yamaguchi; Katsuhisa ; et
al. |
March 25, 2010 |
LASH ADJUSTER
Abstract
A lash adjuster is provided which includes a cylindrical housing
having an open top and formed with an internal thread on an inner
periphery thereof, a screw rod having an external thread formed on
an outer periphery thereof and in threaded engagement with the
internal thread, and a spring biasing the screw rod outwardly of
the housing. Each of the internal thread and the external thread
having a pressure flank configured to receive pressure when a force
that tends to push the screw rod into the housing acts on the screw
rod, and a clearance flank having a smaller flank angle than the
pressure flan. The screw rod has an end protruding from the housing
and configured to support an arm of a valve operating mechanism so
as to be pivotable about this end. Oil film expelling grooves are
formed in the pressure flank of the external thread, using a tap
having a thread that extends so as to cross the internal
thread.
Inventors: |
Yamaguchi; Katsuhisa;
(Shizuoka, JP) ; Bunko; Hiroshi; (Shizuoka,
JP) ; Maeno; Eiji; (Shizuoka, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
39875482 |
Appl. No.: |
12/595856 |
Filed: |
April 10, 2008 |
PCT Filed: |
April 10, 2008 |
PCT NO: |
PCT/JP2008/057092 |
371 Date: |
October 14, 2009 |
Current U.S.
Class: |
123/90.46 |
Current CPC
Class: |
F01L 2810/02 20130101;
F01L 1/22 20130101; F01L 1/185 20130101; F01L 1/2405 20130101; F01L
2305/00 20200501; F01L 2820/032 20130101 |
Class at
Publication: |
123/90.46 |
International
Class: |
F01L 1/18 20060101
F01L001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2007 |
JP |
2007-109499 |
Claims
1. A lash adjuster comprising a cylindrical housing having an open
top and formed with an internal thread on an inner periphery
thereof, a screw rod having an external thread formed on an outer
periphery thereof and in threaded engagement with said internal
thread, and a spring biasing said screw rod outwardly of said
housing, each of said internal thread and said external thread
comprising a pressure flank configured to receive pressure when a
force that tends to push the screw rod into the housing acts on the
screw rod, and a clearance flank having a smaller flank angle than
said pressure flank, said screw rod having an end protruding from
said housing and configured to support an arm of a valve operating
mechanism so as to be pivotable about said end, wherein the
pressure flank of said internal thread has oil film expelling
grooves formed therein to extend in a direction to cross the
direction in which said internal thread extends, said oil film
expelling grooves being formed using a tap having a thread that
extends so as to cross the internal thread.
2. The lash adjuster of claim 1 wherein said oil film expelling
grooves-have a lead angle that differs from a lead angle of said
internal thread.
3. The lash adjuster of claim 1 wherein the helix direction of said
oil film expelling grooves is opposite to the helix direction of
said internal thread.
4. The lash adjuster of claim 1 wherein said oil film expelling
grooves have a bottom diameter larger than an effective diameter of
said internal thread, and wherein said internal thread has an apex
that extends continuously in the direction in which said internal
thread extends.
5. The lash adjuster of claim 1 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal
thread.
6. The lash adjuster of claim 2 wherein said oil film expelling
grooves have a bottom diameter larger than an effective diameter of
said internal thread, and wherein said internal thread has an apex
that extends continuously in the direction in which said internal
thread extends.
7. The lash adjuster of claim 3 wherein said oil film expelling
grooves have a bottom diameter larger than an effective diameter of
said internal thread, and wherein said internal thread has an apex
that extends continuously in the direction in which said internal
thread extends.
8. The lash adjuster of claim 2 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal
thread.
9. The lash adjuster of claim 3 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal
thread.
10. The lash adjuster of claim 4 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal
thread.
11. The lash adjuster of claim 6 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal
thread.
12. The lash adjuster of claim 7 wherein said oil film expelling
grooves have a pitch smaller than a pitch of said internal thread.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a lash adjuster mounted in an
engine valve operating mechanism.
[0002] Many known valve operating mechanisms include an arm that
pivots corresponding to the rotation of a cam, thereby pushing a
valve stem connected to a valve provided at an intake or exhaust
port of an engine and moving the valve.
[0003] When such a valve operating mechanism is thermally expanded
due to increased ambient temperature while the engine is running,
due to differences in thermal expansion coefficient between
component parts of the valve operating mechanism, gaps between the
respective component parts of the valve operating mechanism
(including the gap between the arm and the valve stem) may change,
thus producing noise and causing the valve to be opened and closed
at wrong timing. Also, when the sliding portions of the valve
operating mechanism become worn, gaps between the component parts
of the valve operating mechanism (such as the gap between the valve
and the valve seat) may change, thus producing noise.
[0004] In order to eliminate such changes in gaps between the
component parts of the valve operating mechanism, the pivot point
of the arm is, in many cases, supported by a lash adjuster to
automatically adjust the pivot point of the arm with the lash
adjuster.
[0005] One known lash adjuster of this type includes a cylindrical
housing with an open top, a screw rod having an external thread
formed on its outer periphery and in threaded engagement with an
internal thread formed on the inner periphery of the housing, and a
spring biasing the screw rod outwardly of the housing, with the
protruding end of the screw rod supporting the pivot point of the
arm.
[0006] The external thread formed on the outer periphery of the
screw rod and the internal thread formed on the inner periphery of
the housing both comprises a pressure flank that receives pressure
when a force that tends to push the screw rod into the housing
(hereinafter referred to as "pushing force") is applied, and a
clearance flank having a smaller flank angle than the pressure
flank.
[0007] With this lash adjuster, when pushing force is applied to
the screw rod due to the rotation of the cam, the pressure flank of
the external thread formed on the outer periphery of the screw rod
is supported by the pressure flank of the internal thread formed on
the inner periphery of the housing, so that the screw rod is not
axially movable. When the relative position between the arm and the
valve stem changes due e.g. to thermal expansion of the valve
operating mechanism, the screw rod moves axially in the housing
while rotating, thereby eliminating the changes in gaps between
component parts of the valve operating mechanism.
[0008] In this arrangement, the moment the pressure flank of the
external thread formed on the outer periphery of the screw rod is
supported on the pressure flank of the internal thread formed on
the inner periphery of the housing, any engine oil that exists
between the pressure flanks may form an oil film due to the
squeezing effect. Especially while the ambient temperature is low,
an oil film tends to form between the pressure flanks because the
viscosity of engine oil is high at low temperature.
[0009] If an oil film forms between the pressure flanks, the oil
film dramatically reduces the friction between the pressure flanks.
Thus, when pushing force is applied to the screw rod due to the
rotation of the cam, the screw rod may rotate and be pushed into
the housing. If the screw rod is pushed into the housing, the pivot
point of the arm moves, thus causing the valve to be impulsively
seated on the valve seat and producing noise.
[0010] In order to expel such oil film between the pressure flanks,
a lash adjuster is proposed in which oil film expelling grooves are
formed in the pressure flank of the external thread formed on the
outer periphery of the screw rod so as to extend parallel to the
external thread (JP3-501758A). For the same purpose, in another
lash adjuster, axial grooves are formed by broaching in the
internal thread formed on the inner periphery of the housing to
divide the internal thread into a plurality of separate portions
(JP2000-130114A). In these lash adjusters, engine oil present
between the pressure flanks is expelled into the oil film expelling
grooves, thereby preventing formation oil film between the pressure
flanks.
[0011] In the case of the former lash adjuster, because the oil
film expelling grooves are formed parallel to the thread, the oil
film expelling grooves are long, so that engine oil in the oil film
expelling grooves is difficult to flow. This in turn makes it
difficult for engine oil present between the pressure flanks to
flow into the oil film expelling grooves, and thus making it
difficult to effectively prevent formation of oil film between the
pressure flanks.
[0012] For the latter lash adjuster, because the internal thread is
formed by a tap and the oil film expelling grooves are formed by
broaching, a larger number of manufacturing steps are needed, and
thus the manufacturing cost is high. Also, if the internal thread
is axially long, it is difficult to form oil film expelling grooves
by broaching.
[0013] An object of the present invention is to provide a lash
adjuster which can effectively eliminate oil film between the
pressure flanks and which can be manufactured at a low cost.
SUMMARY OF THE INVENTION
[0014] In order to achieve this object, oil film expelling grooves
are formed in the pressure flank of the internal thread, using a
tap having a thread that extends in a direction crossing the
internal thread.
[0015] The thread of the tap may have a lead angle that differs
from the lead angle of the internal thread, whereby the thread of
the tap crosses the internal thread. Alternatively, a tap may be
used of which helix direction is opposite to the helix direction of
the internal thread, whereby the thread of the tap crosses the
internal thread.
[0016] Preferably, the lash adjuster according to this invention
has the following structural features. [0017] 1) The tap has an
outer diameter larger than an effective diameter of the internal
thread, and a root diameter smaller than the effective diameter of
the internal thread. [0018] 2) The thread of the tap has a pitch
smaller than the pitch of the internal thread.
[0019] With the lash adjuster according to this invention, because
the oil film expelling grooves are formed in the internal thread,
using a tap having a thread that crosses the internal thread, each
oil expelling groove has one end thereof open to the apex of the
internal thread. Thus, engine oil in the oil film expelling grooves
can more easily flow. This in turn makes it easier for engine oil
present between the pressure flanks to flow into the oil film
expelling grooves, and thus makes it possible to effectively
eliminate oil film between the pressure flanks. Also, because the
internal thread and the oil film expelling grooves can both be
formed by a tap, it is possible to reduce the number of
manufacturing steps and thus the manufacturing cost.
[0020] In the arrangement in which the helix direction of the
internal thread 21 is opposite to the helix direction of the oil
film expelling grooves 24 so that the thread of the tap crosses the
internal thread, because the internal thread crosses the oil film
expelling grooves at a large angle, it is possible to minimize the
formation of burrs at portions where the respective oil film
expelling grooves intersect the apex of the internal thread.
[0021] In the arrangement in which the tap has an outer diameter
larger than the effective diameter of the internal thread, and a
root diameter smaller than the effective diameter of the internal
thread, it is possible to reliably form the oil film expelling
grooves while keeping the apex of the internal thread intact.
[0022] In the arrangement in which the thread of the tap has a
pitch smaller than the pitch of the internal thread, because the
distance between the adjacent oil film expelling grooves is small,
it is possible to effectively expel oil film between the pressure
flanks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a front view of a valve operating mechanism
including a lash adjuster embodying the present invention;
[0024] FIG. 2 is a sectional front view of the lash adjuster shown
in FIG. 1;
[0025] FIG. 3 is an enlarged sectional view of the housing of FIG.
2 with the screw rod removed; and
[0026] FIG. 4 is an enlarged sectional view of an internal thread
formed on the inner periphery of the housing shown in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] FIG. 1 shows a valve operating mechanism including a lash
adjuster 1 embodying the present invention. This valve operating
mechanism includes a valve 4 provided at an intake port 3 of an
engine cylinder head 2, a valve stem 5 connected to the valve 4,
and an arm 6 pivotally supported by the lash adjuster 1.
[0028] The valve stem 5 extends upwardly from the valve 4 and is
slidably inserted through the cylinder head 2. An annular spring
retainer 7 is fixed to the outer periphery of the valve stem 5 at
its top end. A valve spring 8 is mounted between the bottom surface
of the spring retainer 7 and the top surface of the cylinder head
2. The valve spring 8 biases the valve stem 5 upwardly through the
spring retainer 7, thereby seating the valve 4 on a valve seat
9.
[0029] The arm 6 has one end thereof supported by the lash adjuster
1, and the other end in contact with the top end of the valve stem
5. A roller 10 is mounted to the central portion of the arm 6. The
roller 10 is in contact with a cam 11 provided over the arm 6. The
cam 11 is fixedly mounted around a camshaft 12. When the camshaft
12 rotates, the cam lobe 11b which protrudes from the base circle
11a presses down the arm 6 through the roller 10.
[0030] The lash adjuster 1 is received in a hole 13 formed in the
top surface of the cylinder head 2. As shown in FIG. 2, the lash
adjuster 1 comprises a cylindrical housing 14 having an open top, a
screw rod 15 inserted in the housing 14, a bottom member 16 closing
the bottom end of the housing 14, and a spring 17.
[0031] The spring 17 is mounted between the bottom member 16 and
the screw rod 15 and biases the screw rod 15 outwardly of the
housing 14. The screw rod 15 has a hemispherical end 18 protruding
from the housing 14. The protruding end 18 is received in a recess
19 formed in the bottom surface of the arm 6, and supports the arm
6 so as to be pivotable about the recess 19.
[0032] The screw rod 15 has an external thread 20 formed on the
outer periphery thereof at its lower portion and in threaded
engagement with an internal thread 21 formed on the inner periphery
of the housing 14. The external thread 20 and the internal thread
21 both have an asymmetrical serration-shaped axial section, and
comprises a pressure flank 22 for receiving pressure when force
acts on the screw rod 15 that tends to push the screw rod 15 into
the housing 14, and a clearance flank 23 having a smaller flank
angle than the pressure flank 22.
[0033] As shown in FIG. 3, oil film expelling grooves 24 are formed
in the pressure flank 22 of the internal thread 21 with a tap T
having a helix direction (counterclockwise in the figures) opposite
to the helix direction of the internal thread 21 (clockwise in the
figures). Thus, as shown in FIG. 3, the grooves 24 extend in a
direction that crosses the direction in which the internal thread
21 extends. As also shown in FIG. 3, the grooves 24 are spaced from
each other in the direction in which the internal thread 21
extends. Also, each oil film expelling groove 24 extends to the
apex 21A of the internal thread 21.
[0034] The oil film expelling grooves 24 are formed with a tap T
having an outer diameter larger than the effective diameter of the
internal thread 21 (diameter of an imaginary cylinder 25 where the
width W1 of the thread groove is equal to the width W2 of the
thread ridge), and a root diameter smaller than the effective
diameter of the internal thread 21. Thus, as shown in FIG. 4, the
oil film expelling grooves 24 reliably extend to portions of the
pressure flank where the diameter is larger than the diameter of
the imaginary cylinder 25, while keeping the apex of the internal
thread intact. The pitch of the tap T (i.e. the axial distance
between adjacent oil film expelling grooves 24) is smaller than the
pitch of the internal thread 21.
[0035] In this valve operating mechanism, when the camshaft 12
rotates and the cam lobe 11b of the cam 11 presses down the arm 6,
the valve 4 separates from the valve seat 9, thereby opening the
intake port 3. In this state, although pushing force is applied to
the screw rod 15, because the pressure flank 22 of the external
thread 20 is supported by the pressure flank 22 of the internal
thread 21, the screw rod 15 never moves axially.
[0036] When the camshaft 12 further rotates and the cam lobe 11b
moves past the roller 10, the valve stem 5 moves upward under the
biasing force of the valve spring 8, thus seating the valve 4 on
the valve seat 9, closing the intake port 3.
[0037] While the engine is running, if there exists a difference in
thermal expansion between component parts of the valve operating
mechanism such as the cylinder head 2, valve stem 5 and arm 6, and
the distance between the cam 11 and the arm 6 increases, the screw
rod 15 protrudes while rotating under the biasing force of the
spring 17, thus eliminating a gap between the base circle 11a of
the cam 11 and the roller 10, which in turn prevents impulsive
seating of the valve 4 on the valve seat 9. If the contact surfaces
of the valve 4 and the valve seat 9 become worn, the screw rod 15
is pushed into the housing while rotating under the biasing force
of the valve spring 8, so that the valve stem 5 moves upward until
the gap between the contact surfaces of the valve 4 and the valve
seat 9 disappears.
[0038] In this lash adjuster 1, the moment the pressure flank 22 of
the external thread 20 of the screw rod 15 is supported on the
pressure flank 22 of the internal thread 21 of the housing 14, any
engine oil that exists between the pressure flanks 22 is released
into the oil film expelling grooves 24. This minimizes the
formation of oil film due to the squeezing effect between the
pressure flanks 22, and thus ensures that axial force applied to
the screw rod can be quickly supported by the internal thread 21 of
the housing 14. This in turn makes it possible to reliably prevent
the screw rod 15 from being pushed into the housing even when the
ambient temperature is low and the viscosity of engine oil is
high.
[0039] Further, in this lash adjuster 1, since each oil film
expelling groove 24 has one end thereof extending to the apex 21A
of the internal thread 21, engine oil in the oil film expelling
grooves 24 can more easily flow. Thus, the moment the pressure
flank 22 of the external thread 20 of the screw rod 15 is supported
on the pressure flank 22 of the internal thread 21 of the housing
14, engine oil that exists between the pressure flanks 22 can
easily flow into the oil film expelling grooves 24. Thus, it is
possible to more easily expel oil film between the pressure flanks
22.
[0040] In this lash adjuster 1, because the internal thread 21 and
the oil film expelling grooves 24 are both formed by taps, the
internal thread 21 and the oil film expelling grooves 24 can be
formed in the housing 14 by chucking the housing once. This reduces
the number of machining steps and thus the manufacturing cost.
Also, since the oil film expelling grooves 24 are formed by a tap
T, it is possible to easily form the oil film expelling grooves 24
even if the internal thread 21 is axially long.
[0041] Further, with this lash adjuster 1, since the oil film
expelling grooves 24 are formed using a tap T having a thread of
which the helix direction is opposite to the helix direction of the
internal thread 21, the internal thread 21 crosses the oil film
expelling grooves 24 at a large angle, which minimize the formation
of burrs at portions where the respective oil film expelling
grooves 24 intersect the apex 21A of the internal thread.
[0042] Also, because the pitch of the tap T (i.e. the axial
distance between adjacent oil film expelling grooves 24) is smaller
than the pitch of the internal thread 21, the distance between the
adjacent oil film expelling grooves 24 is small, so that oil film
can be effectively expelled.
[0043] In the embodiment, a tap is used of which the helix
direction of the thread is opposite to the helix direction of the
internal thread so that the thread of the tap crosses the internal
thread 21. But instead, a tap may be used having a thread of which
the helix direction is the same as the helix direction of the
internal thread but of which the lead angle differs from that of
the internal thread 21 so that the thread of the tap crosses the
internal thread 21.
* * * * *